The Injector. The injector may be defined as an apparatus for forcing water into a steam boiler in which a jet of steam imparts its energy to the water and thus forces it into the boiler against boiler pressure. Injectors are now universally employed for delivering the feed water to the boiler. Two injectors are always used, either one of which should have a capacity sufficient to supply the boiler with water under ordinary working conditions. They are located one on either side of the boiler. Injectors may be classified as lifting and non-lifting, the former being most commonly used. The lifting injector is placed above the high water line in the tank, therefore in forcing water into the boiler, it lifts the water through a height of a few feet. The non-lifting injector is placed below the bottom of the water tank, hence the water flows to the injector, by reason of gravitation.
There are a great many different injectors on the market. All work upon the same general principle, differing only in the details of construction. One type only will be described, namely, the Sellers injector illustrated in Fig. 93.
Sellers Injector. To operate this injector, the method of procedure is as follows: Draw starting lever, 33, slowly. If the water supply is hot, draw the lever about one inch and after the water is lifted, draw the lever out the entire distance. The cam lever, 34, must be in the position shown. To stop the injector, push the starting lever in. To regulate the amount of flow of water after the injector has been started, adjust the regulating handle, 41. If it is desired to use the injector as a heater, place the cam lever, 34, in the rear position and pull the starting lever slowly.
The injector is not a sensitive instrument but requires care to keep it in working condition. It should be securely connected to the boiler in easy reach of the engineer. All joints must be perfectly tight to insure good working conditions. All pipes, hose connections, valves, and strainers must be free from foreign matter. Most failures of injectors are due largely to the presence of dirt, cotton, waste, etc., in the strainers. It is not possible to mention in detail all circumstances which produce injector failures but the complaints commonly heard are as follows:
1. The injector refuses to lift the water promptly, or not at all.
2. The injector lifts the water but refuses to force it into the boiler. It may force a part of the water into the boiler, the remainder being lost in the overflow.
Unless these failures are due to the wearing out of the nozzles which may be renewed at any time, they may be largely avoided by keeping in mind the following points:
All pipes, especially iron ones, should be carefully blown out with steam before the injector is attached, the scale being loosened by tapping the pipes with a hammer.
All valves should be kept tight and all spindles kept tightly packed. When a pipe is attached to the overflow, it should be the size called for by the manufacturer.
The suction pipe must be absolutely tight since any air leak reduces the capacity of the injector.
The delivery pipe and boiler check valve must be of ample dimensions.
The suction pipes, hose, and tank valve connections must be of ample size and the hose free from sharp kinks and bends.
The strainer should be large enough to give an ample supply of water even if a number of the holes are choked.
The injector is one of the most important boiler appliances, for upon the ability of the injector to promptly supply the necessary water depends the movement of trains. It is, therefore, very neces- sary to keep the injector in perfect repair by following the hints given above.
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